1. Field of the Invention
This invention relates to a method used in the process of producing grain-oriented electrical steel sheet, particularly to a method for hot rolling a grain-oriented electrical steel slab produced by continuous casting, and still more particularly to a method of hot rolling a grain-oriented electrical steel slab which improves the productivity of grain-oriented electrical steel sheet by enabling maximization of the width of a continuously cast slab of grain-oriented electrical steel.
2. Description of the Prior Art
Grain-oriented electrical steel sheet has superior magnetic properties, specifically high flux density and low core loss, and is therefore widely used as a core material for transformers and the like.
In recent years, a demand has arisen in this field of technology for the supply of grain-oriented electrical steel sheet with even more superior magnetic properties at even lower prices. Thus engineers in this field are being required to find ways for raising productivity and improving yield while at the same time reducing production costs.
With a view to increasing productivity, ensuring reliable material quality and the like, nearly all grain-oriented electrical steel slab is currently produced by continuous casting. Productivity in continuous casting is a function of casting speed and casting size. More specifically, the casting speed is selected to be the highest allowable within the restrictions dictated by the need to maintain stable casting performance. On the other hand, the casting size is selected as that most suitable for the manufacture of products of the desired size in the ordinary hot rolling process. Moreover, since product size varies greatly, it is also necessary to provide the materials for their production in a wide range of sizes and, therefore, the casting size is not necessarily set at the maximum allowable within the restrictions dictated by the need to maintain stable casting performance.
What is required most for upgrading productivity in continuous casting is, therefore, increasing (maximizing) slab width to the largest allowable by the facility capability.
In view of this need, techniques have been proposed for carrying out heavy-reduction edge rolling in the hot rolling step so as to reduce the slab width to that required for the particular product to be manufactured, in, for example, Japanese Published Patent Application Nos. 59(1984)-42561 and 1(1989)-12561 and other publications. Published Application No. 59(1984)-42561 discloses a method for high-yield edging of a wide continuously cast slab by the use of large-diameter edgers in the hot rolling step. On the other hand, Published Application No. 1(1989)-12561 discloses a method for adjusting the composition and slab cooling rate of medium- and low-carbon steels to optimum values for preventing cracking and the occurrence of flaws during heavy-reduction hot rolling.